Preeclampsia remains a leading cause of maternal and perinatal mortality and morbidity worldwide. The disorder is thought to result from chorionic placental ischemia, as a direct consequence of inadequate transformation of the spiral segments of the uteroplacental artery by the invading extravillous cytotrophoblasts. However, the mechanisms regulating trophoblast invasion have not been fully elucidated. Adrenomedullin (AM) is a secreted peptide hormone with multiple activities. AM mRNA has been identified in mouse trophoblast giant cells, which are derived from the concepius and are directly in contact with maternal tissues at the implantation site. AM is highly expressed in cytotrophoblast cells in the human placenta, and the intensity of AM protein expression in placental trophoblasts from preeclampsia was decreased compared with normotensive controls. We have recently demonstrated that AM mRNA and mRNA for AM receptors are expressed by first trimester cytotrophoblasts HTR-8/SV neo cells and human term placental villous tissues. AM substantially enhances HRT-8/SV neo cell invasion, and the invasion-promoting action of AM was blocked by AM antagonist, AM22-52- These observations lead us to hypothesize that AM may regulate trophoblast differentiation along the invasive pathway, and insufficient AM production or reduced AM receptor expression may be involved in impaired implantation. To test these hypotheses, we proposed the following specific aims: Aim 1) to determine the cellular localization of AM and its receptors in human placental villi, and observed their changes at various stages of pregnancy and in preeclampsia; Aim 2) to determine the effects of AM on human first trimester cytotrophoblast proliferation and differentiation; and Aim 3) to examine whether oxygen tension regulates AM-stimulated cytotrophoblast invasions, and if so, whether they are related to trophoblast AM production and AM receptor expression. The present study will provide evidence suggesting autocrine or paracrine modes of AM actions. Our long-term goal is to define the role of AM in the initiation, growth, and maintenance of the human placenta via controls of trophoblast functions. We believe that the completion of these studies may assist in further understanding the physiology of implantation and the pathogenesis of preeclampsia. Knowledge gained from these studies may assist in designing appropriate therapeutic strategies to prevent preeclampsia in the human.